what does that mean for us? >> if the airplane is not all safe and legal, it can't go. >> reporter: the safety checks are inside and out. on united's new 787 dreamliner technicians examine the electronics. >> we're going over some problems we've had in the past. talking about ways we can keep it from happening again. >> reporter: every four years or so, every plane goes through a major safety overhaul. what are th working on here? >> this is a 757. they will completely open the airplane up, inspect everything. replace a lot of components. lubricate everything. put it back together. >> reporter: most mechanical problems are logged in flight to so base crews know what's wrong before the plane lands. it's not always a quick fix. >> they do the best we can. they didn't build it in a day. we can't always fix it in just five minutes. but you always get them fixed. >> reporter: and we're seeing travelers here come in waves. right now it's a little lull. but two hours ago this place was packed. you could see the ticketi